This invention relates to a sheet post-processing device and an image-forming device.
In many cases a sheet post-processing device for piling up and positioning two or more sheets of paper, and for binding the sheets by staples is added to an image-forming device, such as a copying machine, a printer, and a facsimile to discharge a paper bunch on a tray. There are some examples of such sheet post-processing device written in the Provisional-Publication or Kokai Publication No. 2-144370 and the Provisional-Publication or Kokai Publication No. 1-313261. The device written in the publications has a tray separated from the passage of the sheets in the post-processing device. Along the paper discharge direction the upstream portion of the tray is located in lower position than the downstream portion of the tray.
Accordingly, the post-processing device such as prior arts must be larger and expensive, because the tray is separated from the passage of the sheets and the height of the tray largely increases from upstream portion to the downstream portion along the paper discharge direction. And the device sometimes needs an auxiliary belt conveyor between the passage of sheets in the device and the tray in order to prevent the device from dropping the sheets between the passage and the tray during a series of the dealing with the sheets of paper, because the tray is largely separated from the passage. The auxiliary conveyor makes the device larger and more expensive.
This invention was made, after taking the above situations into consideration, the first purpose of this invention is to offer a sheet post-processing device being small and cheap as a whole.
The second purpose of this invention is to offer the image-forming device with the above-mentioned sheet post-processing device.
In order to attain the first purpose of the invention, the following solution techniques are adopted:
A sheet post-processing device for discharging the sheets on a tray as a paper bunch after piling-up and positioning the received sheets comprising:
a conveyance means for conveying the sheets along the predetermined direction which is changeable;
a tray for arranging and loading a paper bunch; and
a holding means for holding a paper bunch tightly;
wherein the holding means is operated when the conveyance means conveys the sheets in the paper discharging direction and is released when the conveyance means conveys the sheets in the paper taking-in direction.
According to the above-mentioned solution technique, the paper received by the conveyance means is conveyed to the tray in the paper discharge direction, however, is turned to the reverse direction to the pilling-up position in the middle of the passage and the back end (the end in the paper discharge direction) of a paper reaches to the pilling-up position. At this position the paper is held by the holding means tightly. The next coming paper is also operated by the conveyance means, however the former sheet or sheets of paper being held by the holding means stay at the piling-up position, while the conveyance means conveys the next paper to the tray in the paper discharging direction. When the predetermined number of sheets of paper are piled up at the piling-up position in this manner to form a paper bunch, the holding function of the holding means will be released and the paper bunch will be conveyed in the paper discharging direction by the conveyance means while the holding means is released.
When the predetermined number of sheets of paper are piled up at the piling-up position, the sheets can be bound by a stapler. To convey the paper in the opposite direction against the paper discharging direction and to position the back end of sheets correctly at the piling-up position, a leading guide which leads the paper from a upper position to a lower position is disposed along the passage of paper formed by the conveyance means, and an arranging support which stretches almost horizontally in the opposite direction against the paper discharging direction from the lower position of the passage is disposed under the leading guide to pile up the back end of the sheets on the arranging support. It may be desirable to form on the end of the arranging support a stopper for positioning the back ends of the sheets.
It is desirable for the conveyance means to have a variable conveyance ability, since the thickness and weight considerably differ from a sheet of paper by a paper bunch. For example, in case the conveyance means is composed of a pair of rollers pinching a sheet or sheets, the power of pinching the sheets by the rollers is changed according to a sheet or sheets. (For example, one roller""s pressing force against the other roller is changed.) A plural roller having a common shaft may be composed of rollers having a large outer diameter and rollers having a small outer diameter, and only rollers having a large diameter will be on a sheet of paper when the sheet is conveyed and both large and small rollers will be on a paper bunch when the bunch is conveyed, wherein the rollers having a large diameter may be made of the soft material being elastic deformable. The diameter of large rollers will be compressed in the direction of the diameter by a paper bunch, when the bunch is conveyed. In order to compress the diameter of the large rollers, it is also possible to set the conveyance means so as to have at least two positions, for example. It is desirable to set the difference between the diameter of the large rollers and that of the small rollers to be more than twice of the thickness of the paper bunch (i.e. the maximum permissible thickness) so that the small rollers do not contact with the bunch when the large rollers are not compressed.
An image-forming device to achieve the second object comprises a previously described sheet post-processing device. The objects of this invention should not be limited to the above-mentioned objects, and include tacitly providing the object described as being substantially preferable or advantageous.